1. Field of the Invention
This invention relates to a stereoscopic display by which a viewer can view a stereoscopic image without using special eyeglasses, and more particularly, to a stereoscopic display by which a viewer can view a stereoscopic image even when the viewer moves forward or backward.
2. Description of the Prior Art
Examples of a conventional device for displaying a stereoscopic image without using special eyeglasses include one in which a parallax barrier or a lenticular lens is arranged on a viewer side of a screen of a display panel such as a liquid crystal display (LCD) panel, so that a stereoscopic image can be viewed by separating light from a right eye image and light from a left eye image which are alternately displayed for every other vertical line on the display screen.
There is also a device for displaying a stereoscopic image without using special eyeglasses where light for a left eye and light for a right eye are separately incident on a transmissive-type display panel such as an LCD panel.
In the above-mentioned stereoscopic displays, an optimum viewing position such as an optimum distance between a viewer and a display, is set depending on a structure of a device. If a viewer moves out of a optimum viewing position, the viewer can not view a good stereoscopic image.
A method for expanding a region, where a viewer can view a stereoscopic image, in back and forth, and right and left directions, has been proposed in Japanese Laid-Open Gazette No. 270745/1995 (IPC:G02F 1/13). A device in this document is provided with means for detecting a viewer""s position and can switch a shading barrier in accordance with a viewer""s movement in back and forth direction with respect to a display panel. To speak more details, laminated elements by an active-barrier method which form and eliminate slits electrically are used as a shading barrier for separating light from a left eye pixel and light from a right eye pixel. Thus, the device in the above document can switch the elements by the active-barrier method to be used in accordance with back and forth movement by the viewer. In order to display a stereoscopic image to a viewer who moves leftward and rightward, the device electrically shifts positions of the slits of elements by the active-barrier method in accordance with the viewer""s right and left movement.
In the above mentioned method, however, the structure becomes complicated and cost is high to realize the structure where the slits are electrically shifted in a horizontal direction. Furthermore, it is very difficult to laminate the elements by the active-barrier method at a real production site. As a result, the cost becomes too high to manufacture such a device.
Although it is possible merely to superimpose a TN type LCD panel or the like instead of laminating the elements, it generates a gap double as thick as a glass substrate used in the LCD panel structurally between shading barriers, and it causes inconvenience in finely adjusting a normal viewing distance.
Other method for detecting a viewer""s head position and expanding a region where a viewer can view a stereoscopic image in accordance with a right and left movement by the viewer has been proposed in Japanese Laid-Open Gazette No. 152668/1997. A stereoscopic picture display device without requiring special eye-glasses, in the document, can expand a region where a viewer can view a stereoscopic image by replacing a right eye image and a left eye image on a display panel of the stereoscopic display in accordance with a position of the viewer""s head, whereby the stereoscopic display enables the viewer to view a stereoscopic image in both stereoscopic region and pseudo-stereoscopic region. The method is effective against the viewer""s movement in a horizontal direction and capable of expanding a stereoscopic viewing region dramatically.
The method, however, is not effective against the viewer""s movement in back and forth direction. The problem occurred when a viewer moves forward and backward has not been solved yet.
A present invention has been made to solve the above mentioned problems and has an objective to provide a stereoscopic display without using special eye-glasses, which can expand a range where a stereoscopic image can be viewed in back and forth directions can be manufactured at a relatively low cost.
A viewer can view a stereoscopic view by using a stereoscopic display according to the present invention, which stripes light and gives the striped light to an LCD panel consisting of a display screen containing a group of left eye pixels and a group of right eye pixels. The stereoscopic display comprises a first light source arranged apart from the LCD panel by a first distance, a second light source arranged apart from the LCD panel by a second distance, a lenticular screen for shrinking striped light images from the light sources and forming the striped light images at the same interval and arranged in front of the first and second light source, a first diffusing means for diffusing and transmitting light and forming a striped light image from the first light source, a second diffusing means for diffusing and transmitting light and forming a striped light image from the second light source, wherein a distance of an optimum viewing from which a viewer can view a stereoscopic image can be changed by switching between a state where the first light source is on and the first diffusing means has a diffusing effect and a state where the second light source is on and the first diffusing means has a diffusing effect.
A dispersion type LCD panel can be used for the diffusing means.
Letting E be an interval between a viewer""s pupils, P be an interval between pixels of a LCD panel, C be a distance between the LCD panel and the diffusing plate which forms a striped light image from the light source, an optimum viewing distance D satisfies D=C(Exe2x88x92P)/P.
As described above, a normal viewing distance can be expanded in back and forth directions by selecting and switching the first and second light sources and the first and second diffusing means.
The first and second light sources may consist of a first light source for giving a stereoscopic image to a viewer who is in a certain position and a second light source for giving a stereoscopic image to a viewer who is in a position apart in a horizontal direction by approximately a half of a distance between the viewer""s pupils from the certain position.
In the stereoscopic display according to the present invention, the above mentioned two systems of the light sources are switched to be turned on and off corresponding to a position of the viewer.
The optimum light source is turned on corresponding to a position of the viewer and an image to be displayed on the LCD panel is switched, whereby the viewer can view a stereoscopic image from any position regardless of a movement in a horizontal direction of the viewer.